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MECHANISM OF THE TRANSFORMATION OF PRESSURE FLUCTUATION PRODUCED BY KARMAN VORTEX SHEDDING INTO NOISE

卡门涡旋脱落产生的压力脉动转化为噪声的机理

基本信息

批准号：
03650149
负责人：
FUKANO Tohru
金额：
$ 1.34万
依托单位：
KYUSHU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1991
资助国家：
日本
起止时间：
1991 至 1992
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-03650149/
关键词：
Noise Discrete Frequency Noise Karman Vortex Broad Band Noise Uniform Flow Field Rotating Flow Field 圧力変動 NACA翼

项目摘要

It is theoretically and experimentally investigated that the generated noise is closely related with the characteristics of the velocity fluctuation in the near wakes of a blade,NACA 0008 or NACA 0015 placed in a uniform oncoming flow,and in the near wake of a rotating flat plate. The results are summarized as follows:(1)In the case of a thicker blade,NACA 0015,the discrete frequency noise is generated if the attack angle theta is less than about 5 degree. The flow on the pressure side, separates in this case just upstream of the trailing edge of the blade and the Karman vortex street generates,which is the cause to generate the discrete frequency noise. (2)In the case of a thinner blade,NACA 0008,the DFN does not occur if theta=0,because there is no location where adverse pressure gradient is intense. However if there is some attack angle,even if it is small,the flow separates near the leading edge of the blade due to its relatively sharp geometry. Then discrete frequency noise generates. (3)In the case of NACA 0008 blade periodic velocity fluctuation is actually generated relatively far from the blade trailing edge,the DFN,however,does not occur. The reason of this is the flow attached up to the blade trailing edge. This fact shows clearly that the necessary condition of the generation of DFN is the existence of a large dead flow region in the near wake. (4)Although the oncoming flow is sheared in the span direction as in the case of the rotating flow field,DFN occurs. This means the mechanism of the generation of DFN is fundamentally the same that in the uniform main flow. (5)The broad band nature of the spectrum of noise generated from the rotating flat plate can be theoretically explained by the physical model in which the tonal noises are generated locally by the periodic velocity fluctuations due to each Karman vortex shedding and they are integrated in the blade span direction.

理论和实验研究表明，噪声的产生与均匀迎流中NACA 0008或NACA 0015叶片近尾迹的速度脉动特性以及旋转平板近尾迹的速度脉动特性密切相关。结果表明：(1)对于较厚的NACA 0015叶片，当攻角θ小于约5度时，产生离散频率噪声。在这种情况下，压力侧的流动正好在叶片后缘的上游分离，并产生卡门涡街，这是产生离散频率噪声的原因。(2)对于较薄的叶片，NACA 0008，当theta=0时，不会出现DFN，因为没有不利压力梯度强烈的位置。然而，如果有一定的攻角，即使攻角很小，由于其相对陡峭的几何形状，流动也会在叶片前缘附近分离。然后产生离散频率噪声。(3)对于NACA 0008叶片，其速度脉动实际上是在离叶片尾缘较远的地方产生的，但不会产生DFN。这是因为气流附着在叶片尾缘上。这一事实清楚地表明，DFN产生的必要条件是在近尾迹中存在大的死流区。(4)与旋转流场情况一样，迎面流在跨度方向发生剪切，但仍存在DFN现象。这意味着DFN的产生机制与均匀主流的产生机制基本相同。(5)旋转平板产生的噪声频谱的宽带特性可以用物理模型来解释，在该物理模型中，音调噪声是由每个卡曼涡脱落引起的周期性速度脉动局部产生的，它们在叶片跨度方向上积分。